Dehumidifier design

clodpitt

New member
Joined
27 Jan 2005
Messages
3
Visit site
Hi,
I'm a product designer working for a UK manufacturer and my latest project involves the design of a dedicated boat dehumidifier. We are currently generating ideas and concepts and any feedback would be appreciated.
A couple of questions to get started:
Are compressorless systems up to the job when boat is in use?
Any ideas for features? ie stowable, tough compact design, carry handle, timed control.
thanks
 

lydiamight

Well-known member
Joined
9 Feb 2004
Messages
1,101
Location
North West Kent
Visit site
Don't make it too tall. Most boat owners will want to leave it on the galley work surface so that it can drain into the galley sink. Lockers and cupboards often restrict the clear height above the worktops and most existing dehudmidifiers are too tall to fit there.
 
A

Anonymous

Guest
What sort of 'compressorless' system did you have in mind?

As for features, all of those you mentioned are essential plus light weight and QUIET!

Another issue is short-cycling where the unit switches itself off, humidity sensor detects high humidity then switches on again, all in the space of ten minutes or so. What happens with both of ours (different designs) is that the moisture due to the water in the reservoir, on the evaporator, and other parts raises the humidity local to the unit even though the room humidity is low. This turns the machine on, the fan starts, dry room air passes over the sensor and it turns off again. We find that the constant on/off cycle disturbs our sleep and we would rather have it permanently on, but this makes us wake up feeling dry. The answer is to keep the fan running all the time and just cut the compressor in and out. I am going to modify one...funnily enough, by coincidence, I had decided to do that when I awoke this morning before reading your message.

David
 

AndrewB

Well-known member
Joined
7 Jun 2001
Messages
5,860
Location
Dover/Corfu
Visit site
A dehumidifier which could be used away from mains power would be a real blessing, specially for UK winters.

But the key is efficiency. 12v compressor types for boats do exist, but struggle to extract a meaningful quantity of moisture at reasonably low power consumption, given they must be on continuously. For example this one claims to extract 0.38 litres daily consuming 65W, which could imply 130Ah daily at 12v, more than the capacity of a large leisure battery. To keep up with this for extended periods one would need several wind generators fitted! So you probably need to design a dehumidifier which is fuel rather than electric powered, yet safe to leave unattended for long periods.

Incidentally while 0.38 litres daily might be quite adequate for an unattended yacht, it wouldn't be when people are staying aboard - two people can easily breathe and sweat out a couple of litres daily.

The only other type of dehumidifier I know of are those using deliquescing silica crystals, but the amount of water these extract is puny and they have to be dried out and replaced at very frequent intervals - I doubt there is a realistic solution in this direction.
 

Trevethan

New member
Joined
26 Feb 2002
Messages
1,152
Location
Singapore
Visit site
I want one that I can shove in the engine bay. You should be able to duct air in from one area and blow it somewhere else. It should have a 1-2 kilowatt heating element so I can get rid of teh fan heater.

Sepereately mounted humidistat

Frugal with power and able to ciculate air as well as dehumidify.

I'd be happy for it drain into my bilges and get the auto pump take care of it, but suggest a float switch and pump option that could send water over the side/into sink drain etc.

Coulrse the other solution is a dirty great 12 volt fan system with humidistat that pumps wet air out of bilge/low areas to allow drier air from outside in
 

clodpitt

New member
Joined
27 Jan 2005
Messages
3
Visit site
Would a remote fan with integral humidity sensor be useful? This would also help air flow in the worst areas of the boat.
I suppose most dehumidifiers are designed for the home and can be positioned further away away from the bedroom.
The compressorless systems I had in mind were peltier or TEC cooling devices (less extraction) and the silica absorbtion method (less efficient).
 

Shanty

Member
Joined
20 Jan 2002
Messages
771
Location
Scotland - Black Isle
Visit site
Two major problems with existing compressor driven dehumidifiers:

1) power consumption - current models aren't quite frugal enough to run off the boat's 12v system on anything much under superyacht size

2) efficiency at low temperatures - a machine with an advertised respectable output at 20 - 30 deg C will give a very limited output at temperatures below 10 deg C.

A recent thread on this forum talked about a compressorless machine that used a rotating disc containing a dessicant. This overcame problem 2, but did nothing for problem 1. Might be worth investigating nevertheless.
 

Colvic Watson

Well-known member
Joined
23 Nov 2004
Messages
10,891
Location
Norfolk
Visit site
1. Short and squat with attachment points - to fit on sink

2. With heating element to raise cabin temp

3. 240v because 12v is just never going to be feasible (massive battery power needed), makes it too expensive to manufacture and most marina's have shore power.

4. Quiet

5. Built in timer function

6. And don't charge us 'marine' prices.


Meet those requirements and I suspect that there is a big market
 

richardandtracy

New member
Joined
27 Jun 2002
Messages
720
Location
Medway, UK
Visit site
A quiet fuel powered one could be powered by a Stirling engine. Not having an internal explosion every cycle they tend to be quieter. However there are almost no off the shelf Stirling engines & a design just for one application would make it prohibitive.

Regards

Richard.
 

enterprise

New member
Joined
21 Dec 2001
Messages
1,038
Location
MDL Torquay
Visit site
The compresorless design works great, quiet & more efficient at low temperatures.

I bought one of these(link below) & have tested it aboard our boat.
I am delighted with the results.
We only paid half of the advertised cost in the January sales at B&Q at which point I posted my find on this forum under, AMBERDRY Dehumidifiers.
After only a few weeks operating aboard I now have a very dry & comfortably warm cabin for the same price as a compressor alternative.

Now I know compressor units have there die hard fans but not having used one I cannot compare the results between the two, only to say that the compressorless one while doing much the same job as a conventional type has the added bonus of lightness,heat & quiet opperation.

The humidistat is user adjustable which is probably more to do with personal preference.

The physical dimensions as said in a previous post could be better, a more compact unit would be desirable.
How about a factory built in unit that hides the main workings, using ducting to circulate the air through the unit.
A dedicated skin fitting instead of the "perched on the galley" arrangement would also be a bonus

The price should also be closer to the compressor equivalent.
If you search through this site link you will also find reference to a marine version called Rubydry but as far as I can make out it is the same as the amberdry just £50quid dearer???

http://www.dry-it-out.com/amberdry.htm /forums/images/graemlins/grin.gif
 
A

Anonymous

Guest
I cannot visualise how you could have a 'remote fan'. Thinking of a compressor unit, the fan draws room air over the evaporator where it is chilled, and moisture condenses, then, immediately downstream of the evaporator the air passes over the condenser where it is warmed to a slightly higher temperature than room temp (due to the appearance of the latent heat of evaporation and losses in the compressor). There isn't any scope to make this 'remote' - or am I missing something?

Peltier would be very inefficient and would result in a high temperature rise. You might get a lot of enthusiasm for such a system today, in the UK, on a cold January day, but dehumidifiers need to work in other parts of the world at in the summer as well, on occasions.

The dessicant disc type will not work well in higher ambient temperatures and would be inappropriate in any case because of the temperature rise.
 

TrueBlue

Well-known member
Joined
30 Apr 2004
Messages
4,476
Location
Sussex
Visit site
I leave the windows open and suggest a punkah wallah to circulate the air, butthen I have the wrong sort of boat.
 

clodpitt

New member
Joined
27 Jan 2005
Messages
3
Visit site
I was thinking of an extra fan to be positioned away from the main unit - the fan would give the option to target areas (damp corners) away from the airflow produced by the main unit. If a humidistat was located on this fan the main unit could have extra feedback from this position and adjust it's performance accordingly. This would also avoid the nuisance switching you talked about when pockets of air local to the main unit are dry. I agree with your thoughts on peltier and disc type units.
 
Top